Photographic emulsion containing fog inhibitors



Patented Apr. 10, 1934 UNITED STA ES PATENT. OFFICE PHOTOGRAPHIC EMULSION CONTAINING:v FOG INHIBITORS Samuel E. Sheppard and Waldemar Vanselow, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application January 4, 1933, Serial No. 650,136

9 Claims.

15 Usually, the more powerful the sensitizer, the

greater is the tendency to fog. While such fogging action is associated with the speed of inception of the latent image, nevertheless, apparent fog, with its attendant loss in the commercial 7 valueof the product, must be avoided.

' The object of the present invention is to provide a series of compounds for the purpose of stabilizinglight-sensitive materials and thereby correcting the tendency to fog without markedly 5 retarding the sensitivity of the light-sensitive materials. Other objects will hereinafter appear. The photographic sensitivity of silver halide emulsions islargely conditioned by the formation'in the halide grain of very small specks of silver sulfide, silver or both, or analogous bodies. We have found that the production of chemical fog, which is otherwise known as inherent emulsion fog, is probably due to these nucleibecoming excessively large, whereby spontaneous reducibility is brought about.

Sheppard and Hudson, in the Photographic- Journal, Vol. 67, page 359 (1927), have shown in the thioanilides a class of bodies which have either sensitizing or anti-sensitizing and fog in- 9 hibiting properties according. as they react to form silver sulfide or combine with the silver bromide to form a stable non-reducible body.

While the theory of sensitivity restraint and fog inhibition is not essential to the practical application of our discovery, it exhibits the rea-' soning by which we were led to it. Proceeding from these conceptions, 'we have sought for substances which could combine with the silver halide, particularly at the boundary of a growing silver sulfide or other sensitizing speck.

We have now found a class of anti-sensitizing or fog-inhibiting compounds which are effective for the manufacture of such emulsions. This.

class of compounds consists of the thio-pyrazolones containing a hydrogen atom in the 4-position or in the 1-position, that is, in a position adjacent to the carbon atom to which the sulfur is attached. Examples of these thio-pyrazolones are 1-phenyl-3-methyl-5-thio-pyrazolone, which has the structural formula t and 1 phenyl 2-3 dimethy1-5-thio-pyrazolone, which has the structural formula HiC.CN.C

Thio-pyrazolones no longer having a hydrogen atom in either the 4-positon or the 1-position were found not to have anti-fogging properties.

Our theory isthat the fog-inhibiting effect of the thio-pyrazolones is due to the formation of a silver complex having the tautomeric structure in the 1- and 5-positions. This would account for the absence of the fog-inhibiting property in thio-pyrazolones not having a hydrogen atom in the 1- or 4-position, since these compounds would not be capable of forming the silver complex.

Photographic. emulsions containing our novel fog-inhibiting agents are very stable at relativelyhigh temperatures and over a considerable range of hydrogen ion concentration.

In order thoroughly and uniformly to incorporate the anti-fogging agent into the emulsion it is usually necessary to dissolve the material in a suitable solvent such as water or alcohol, or

acetone. Other solvents or mixtures of them, which are compatible with the emulsion, may, of course, be used, but we have found the above solvents to be most desirable.

The proportions in which these compounds are llO incorporated in the emulsions, or in the colloids for the emulsion, are important. Too much of them will often desensitize the emulsion. The maximum proportions which can be used prac- 5, tically, vary slightly with the particular thiopyrazolone which is selected, with the ratio of gelatin to silver halide in the emulsion, with the type of emulsion as regards grain size and alkalinity, with the amount of natural sensitizer also present in the gelatin when the latter is manufactured, with the particular silver halides employed, or with the fog standards which are set by the emulsion manufacturer. The optimum proportion is readily determined by routine test.

.With gelatin-silver halide developing-out emulsions, it is generally advantageous to add from 0.01 gram to 10 grams of the restraining substance per 1000 grams of gelatin. Where gelatin is used in more than one operation, as for example in small amounts for precipitation, and in larger amounts at later meltings, these gelatins may be differentially treated with the.

restraining bodies, as will be understood by those skilled in the art.

Our present fog-inhibiting compounds are effective inall kinds of emulsions ordinarily met with, such as orthochromatic, panchromatic, or X-ray, as well as the ordinary non-color sensitized ones. They can be added without or with sensitizing dyes, or before or after them. Alternatively, the fog inhibiting agent may be used as a solution for treating the finished photographic material.

Our present stabilizing substances may be, in general, incorporated in the emulsions or in the colloids for the emulsions in the same way as the sensitizing substances set forth in United States Patent No. 1,574,944. For example, a mixed silver bromide and iodide emulsion in gelatin may be prepared as setforth in said patent, page 3. After the emulsion is prepared, it may be melted and the proper amount of stabilizing compound thoroughly mixed into it. This mixing is conveniently effected by dissolving the stabilizing substance in a suitable solvent or mixture of solvents, and then stirring such solution into the emulsion.

While our novel fog-inhibiting compounds are preferably used with gelatin, they nevertheless have utility with emulsions made in other colloids such as agar-agar, albumins, gums like gum arabic, or cellulose derivatives. Our compounds likewise have utility in emulsions in which different kinds of silver salts are present, such as silver bromide, silver iodide, silver chloride, or mixtures of any of these with one or more of the others.

Various changes may be made, therefore, in the method of compounding our stabilizing materials with the colloids for the photographic emulsion, and known equivalents may be used therefor without in any way departing from our invention or sacrificing any of the advantages derived therefrom.

As some of the compounds specified herein have individually valuable properties, when used in photographic emulsions, in addition to those which we have pointed out, we consider as included in our invention the use of the class of compounds mentioned and of the individual members=of that class, for whatever purpose in connection with photographic emulsions, particularly in gelatino-silver-halide emulsions, and we consider as included in our invention all modifications and equivalents properly falling within the terms of the appended claims.

What we claim as our invention and desire to be secured by Letters Patent of the United States is:

1. A photographic emulsion comprising a colloid, particles of a photographic silver salt suspended therein, and, as a fog-inhibiting agent, a thio-pyrazolone containing a hydrogen atom in a position adjacent to the carbon atom to which the sulfur is attached.

2. A photographic emulsion comprising a colloid, particles of a photographic silver salt suspended therein, and, as a fog-inhibiting agent, a substituted thio-pyrazolone containing a. hydrogen atom in a position adjacent to the carbon atom to which the sulfur is attached. I

3. A photographic emulsion comprising a. colloid, particles of a photographic silver salt suspended therein, and 1-phenyl-3-methyl-5-thiopyrazolone as a fog-inhibiting agent.

4. A photographic emulsion comprising a colloid, particles of a photographic silver salt suspended therein, and 1 -phenyl-2:3-dimethyl-5- thio-pyrazolone as a fog-inhibiting agent.

5. A gelatino-silver; halide emulsion comprising a thio-pyrazolone containing a hydrogen atom in a position adjacent to the carbon atom to which the sulfur is attached.

6. A gelatino-silver halide emulsion comprising a substituted thio-pyrazolone containing a hydrogen atom in a position adjacent to the carbon atom to which the sulfur is attached.

7. A photographic emulsion comprising gelatin, particles of a photographic silver salt suspended therein, and, from 0.01 gram to 10 grams, per lOOOgrams of gelatin, of a thio-pyrazolone containing a hydrogen atom in a position adjacent to the carbon atom to which the sulfur is attached. 8. A photographic emulsion comprising gelatin, particles of a photographic silver salt suspended therein, and from 0.01 gram to 10 grams, per 1000 grams of gelatin, of 1-phenyl-3-methyl- 5-thio-pyrazolone.

9. A photographic emulsion comprising gelatin, particles of aphotographic silver salt suspended therein, and from 0.01 gram to 10 grams,

per 1000 grams of gelatin, of 1-phenyl-2z3-dimethyl-5-thio-pyrazolone.

SAMUEL E. SHEPPARD. WALDEMAR VANSELOW. 

